Fluid pumping using electric linear motor

ABSTRACT

A drilling fluid pump system includes a plurality of modular pump units that are each driven by a linear electric motor. A control system that can include positional feedback information which is used to control all of the linear motors in the pump system and reduce pressure pulsation. The linear motors can be controlled to reduce fluid pressure pulsation by controlling velocity and relative timing between pistons. To accommodate removal and addition of individual pump units the pump modules can be isolated electrically and hydraulically. This can improve scalability, reliability, and serviceability of the pump system.

REFERENCE TO RELATED APPLICATION

This application claims the benefit of and incorporates by referenceU.S. Provisional Patent Appl. Ser. No. 62/665,039 filed on May 1, 2018.

TECHNICAL FIELD

The present disclosure relates to systems and methods for drilling fluidpumping. More specifically, the present disclosure relates to a drillingfluid pump designs with a linear actuated motor.

BACKGROUND

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present disclosure,which are described or claimed below. This discussion is believed to behelpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

In order to meet consumer and industrial demand for natural resources,companies often invest significant amounts of time and money in findingand extracting oil, natural gas, and other subterranean resources fromthe earth. Particularly, once a desired subterranean resource such asoil or natural gas is discovered, drilling and production systems areoften employed to access and extract the resource. These systems may belocated onshore or offshore, depending on the location of a desiredresource. Further, such systems generally include a wellhead assemblymounted on a well through which the resource is accessed or extracted.These wellhead assemblies may include a wide variety of components, suchas various casings, valves, pumps, fluid conduits, and the like, thatcontrol drilling or extraction operations.

As will be appreciated, drilling and production operations employfluids, referred to as mud or drilling fluids to provide lubrication andcooling of the drill bit, clear away cuttings, and maintain desiredhydrostatic pressure during operations. Mud can include all types ofwater-based, oil-based, or synthetic-based drilling fluids. Mud pumpscan be used to move large quantities of mud from surface tanks, downthousands of feet of drill pipe, out nozzles in the bit, back up theannulus, and back to the tanks. Operations come to a halt if the mudpumps fail, and thus, reliability under harsh conditions, using alltypes of abrasive fluids, is of utmost commercial interest.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in determining orlimiting the scope of the claimed subject matter as set forth in theclaims.

According to some embodiments, a pump system is described that isconfigured to pump fluid (e.g. drilling mud, circulation fluid, orfracturing fluid) down a wellbore. The system includes: anelectrically-powered linear motor including a stationary portion and amoving portion. The moving portion is adapted to move in a reciprocatingfashion relative to the stationary portion. The pump system alsoincludes a pump assembly that has a piston and one or more valvesconfigured to pump a fluid into a wellbore. The reciprocating movingportion drives the piston. According to some embodiments, the pumpsystem also includes a sensor configured to detect movement and/orposition of at least a portion of the motor and/or pump assembly and tooutput position information; and a control system. The control system isconfigured to: control the motion of linear motor; receive the positioninformation; and to make adjustments the control based on the positioninformation thereby reducing error in the motion. According to someembodiments, the control system can be configured to reduce flowpulsation of fluid pumped by the pump system based at least in part onthe position information. According to some embodiments, the pump systemfurther includes a pressure sensor configured to detect discharge fluidpressure of the pump system and output pressure information. Thereduction in flow pulsation of fluid pumped by the pump system is can befurther based in part on the pressure information.

According to some embodiments, the motor and pump assembly together forma first pump unit, and the system further includes one or moreadditional pump units. The control system can be further configured toadjust the relative timing of each motor based on a total number of pumpunits in the pump system.

According to some embodiments, the moving portion is rod-shaped and thestationary portion is tube-shaped and surrounds the rod-shaped movingportion. In such cases the rod-shaped moving portion can be verticallyoriented such that is moves in a vertical direction. According to someother embodiments, the moving portions and the stationary portions arerectangular and planar in shape, and the stationary portion includes twoplanar portions disposed on either side of and sandwiching the movingportion. The moving portion can be configured to move primarily inhorizontal direction. According to some embodiments, the pump unit canbe dual-action, whereby the same linear motor drives a second pumpassembly that includes a second piston and a set of second valvesconfigured to pump the fluid into the wellbore.

According to some embodiments, a plurality of isolation valves arepositioned and configured to hydraulically isolate either of the pumpassemblies thereby facilitating servicing and/or replacement of pumpsystem components without loss of pump system operation.

According to some embodiments, a method of pumping a fluid into awellbore is described. The method includes: controlling a firstelectrically-powered linear motor that includes a stationary portion anda moving portion, such that the moving portion moves in a reciprocatingfashion relative to the stationary portion and drives a first pumpassembly that includes a piston and one or more valves, thereby causinga the fluid to flow into the wellbore; receiving position informationfrom a sensor configured to detect movement and/or position of at leasta portion of the motor and/or pump assembly; and adjusting thecontrolling based at least in part on the position information, therebyreducing error in controlling the position.

As used herein, the terms “drilling mud” “drilling fluid” and “mud” aresynonymous and refer to any of a number of liquid and gaseous fluids andmixtures of fluids and solids (as solid suspensions, mixtures andemulsions of liquids, gases and solids) used in operations to drillboreholes into the earth. Drilling mud includes various categories offluid including: (1) water-base, (2) non-water-base, (3) gaseous(pneumatic), and any combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject disclosure is further described in the following detaileddescription, and the accompanying drawings and schematics ofnon-limiting embodiments of the subject disclosure. The featuresdepicted in the figures are not necessarily shown to scale. Certainfeatures of the embodiments may be shown exaggerated in scale or insomewhat schematic form, and some details of elements may not be shownin the interest of clarity and conciseness.

FIG. 1 is a schematic diagram illustrating a well system that utilizes amud pump system actuated by one or more linear electric motors,according to some embodiments;

FIG. 2 is a perspective view of an array of linear motor actuated pumpunits configured to pump drilling mud, according to some embodiments;

FIGS. 3A, 3B, 3C and 3D are a perspective view, side view, exploded viewand cross section of a linear motor actuated mud pump unit, according tosome embodiments;

FIG. 4 is a diagram illustrating suppling power and control to a linearservo motor configured to actuate a pump unit, according to someembodiments;

FIGS. 5A and 5B are plots showing examples of piston velocity profilesfor a precisely controlled pump piston, according to some embodiments,and conventional crankshaft driven pump piston according to prior art,respectively;

FIG. 6 is a block diagram illustrating power and control systemsassociated with a modular pumping system that include a plurality ofpump units, according to some embodiments;

FIGS. 7A, 7B, 7C and 7D are a perspective view, a top view, and twocross sections of a linear motor actuated mud pump unit, according tosome embodiments; and

FIGS. 8A, 8B, 8C and 8D are a perspective view, a top view, and twocross sections of a linear motor actuated dual-action pump unit,according to some embodiments.

DETAILED DESCRIPTION

One or more specific embodiments of the present disclosure will bedescribed below. These described embodiments are only exemplary of thepresent disclosure. Additionally, in an effort to provide a concisedescription of these exemplary embodiments, all features of an actualimplementation may not be described in the specification. It should beappreciated that in the development of any such actual implementation,as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure. Like referencenumerals are used herein to represent identical or similar parts orelements throughout several diagrams and views of the drawings.

Conventional reciprocating pumps convert rotational motion to linearmotion, utilizing conventional mechanical power transmission methods. Insome applications, an AC induction motor can be connected to a smallsheave that turns a larger sheave mounted to the pinion shaft via abelt. The gear on the pinion shaft meshes with a gear on the crankshaft.The crankshaft is connected to the pistons via connecting rods, whichare timed on the crankshaft using equivalently spaced lobes, and acrosshead system. The connecting rods and crossheads are where therotary motion of the AC motor is converted to purely linear motion. Thepistons reciprocate forward and backward, pushing the drilling fluidthrough the drillstring and downhole.

There are many costly, complex parts that are required to convert rotarymotion to linear motion. Each component has specific maintenancerequirements which require time to perform and have potentially majorconsequences if they are not performed both regularly and correctly,including non-productive time and/or catastrophic failure of theinternal components of the pump.

For optimal function and long component life, proper alignment of theinternal components of drilling fluid pumps, like know triplex pumps, isimportant. Unfortunately, it is also difficult and time consuming. Agreat deal of time is thus spent aligning the pump, and if the pump isnot aligned correctly, contamination of the power end (pinion,crankshaft, crosshead, bearings) is likely to occur. This contaminationof mud and water can shorten the life of the power endcomponents-bearings, gears, etc. Additionally, if alignment isincorrect, the piston life might also be reduced, causing additionalnonproductive time.

In a known application of a reciprocating pump system to pump drillingfluids, triplex reciprocating pumps are used that typically consist ofthree cylinders per mud pump with similar parts. If any cylinder hasparts that need to be replaced, all cylinders are unable to operate. Inorder to avoid any production downtime, there are typically 2-3 mudpumps per rig with the second or third pump sitting idle as a backuppump. Triplex mud pumps may also typically have high pulsation (flowvariation), and require a pulsation dampener to dampen the pulses.

According to some embodiments, a mud pump system is described thatincludes a plurality of pump units. Each pump unit includes a fluidpumping piston assembly that is driven by a linear servo motorservomechanism. According to some embodiments, the servomechanismcomprises a motion controller, synchronous linear motor and linearposition sensor. The pump system design allows each pump unit/piston tobe a separate isolatable module. This contrasts to conventional triplexor similar pumps wherein none of the pistons can be isolated due to: (1)all pistons being tied to a crankshaft; and (2) all pistons being drivenby a single motor. According to some embodiments, in the described mudpump system each piston has its own motor, and can be completelyisolated and bypassed if an issue arises and it needs to be serviced.The pump system design described here thus allows modularity since itenables the addition and removal of any number of pistons or pump unitsfrom the pump system as may be needed for the particular rig. Forexample, if more flow is needed, the pump system described herein couldbe retrofitted with additional cylinder assembly(ies)/pump units toadequately provide the needed flow volume. Alternatively, such flowcapacity can also be reduced by removing unnecessary pump cylindersassembly and servo motors (pump units).

According to some embodiments, the pump system described herein might besupplied with high flow, low pressure fluid via a charge pump. Fluidsmight be drilling fluids such as mud or slurry. During the suctionportion of the cycle, the rod on the linear motor which is connected tothe piston rod will travel upwards opening the suction valve and pullingthe fluid into the liner. Once it reaches the top of the stroke, themotor will push the rod downwards which closes the suction valve, opensthe discharge valve and pushes the fluid out of the module, through thedrillstring, and downhole. The position, speed, and acceleration of eachpiston assembly can be coordinated in such a way as to minimize fluidpulsation through the use of a programmable logic based motioncontroller, linked to an operator's human machine interface in thedrilling control room. Although much of the pump systems are shown anddescribed herein as configured for pumping drilling mud, according tosome embodiments, the pump systems can be used in other drilling,circulation, fracturing operations or in any operation where fluids needto be pumped downhole. Any and all of the pump systems shown anddescribed herein can be applied to any of such pumping applications.

FIG. 1 is a schematic diagram illustrating a well system that utilizes amud pump system actuated by one or more linear electric motors,according to some embodiments. The well system 100 can be configured toextract various minerals and natural resources, including hydrocarbons(e.g., oil and/or natural gas), or configured to inject substances intoan earthen surface 103 and a subterranean earthen formation 105 via awell or wellbore 112. In some embodiments, the well system 100 island-based, such that the surface 103 is a land surface, or subsea, suchthat the surface 103 is a sea floor. In the embodiment of FIG. 1, wellsystem 100 generally includes a drilling rig or platform 120 disposed atthe surface 103, a well or drill string 122 extending downhole from rig120 through wellbore 112, a bottomhole assembly (BHA) 124 coupled to thelower end of drill string 122, and a drill bit 126 attached to the lowerend of BHA 124 and disposed at a lower end of the wellbore 112. Thoughthe description herein may primarily refer to a drill string, it isunderstood that other types of well or tool strings can extend into thewellbore 112.

In this embodiment, well system 100 further includes a mast 128, atraveling block 130, a standpipe 132, a fluid line or mud return line134, a mud tank 136, and a mud pump system 138. The drill string 122 issuspended from travelling block 130, which is in turn supported by mast128. Drilling fluid is pumped using mud pump system 138 into an upperend of drill string 122 via pump discharge pipe 152 and standpipe 132,where the drilling fluid is pumped through a passage of drill string 122down to the drill bit 126. The drilling fluid is pumped through ports inthe drill bit 126 and recirculated to the surface 103 through an annulusof wellbore 112, formed between an inner surface 114 of the wellbore 112and an outer surface of drill string 122. At the surface 103, therecirculated drilling fluid is flowed through the mud return line 134into the mud tank 136. Mud pump system 138 is configured to pumpdrilling fluid disposed in mud tank 136 using pump inlet pipe 150 backto the standpipe 132 using pump discharge pipe 152, such that thedrilling fluid may be flowed back into the passage of the drill string122. Well system 100 may further include other components, such as shaleshakers, for removing entrained cuttings and other debris in therecirculated drilling fluid passing through mud return line 134 prior tobeing flowed back into the standpipe 132 by mud pump system 138. As willbe discussed further herein, in various embodiments, mud pump system 138is driven by a linear electric motor.

FIG. 2 is a perspective view of an array of linear motor actuated pumpunits configured to pump drilling mud, according to some embodiments.The mud pump array 210 shown in this example includes five mud pumpunits 220, 222, 224, 226 and 228, and can form part of mud pump systemfor use in a well drilling system, such as mud pump system 138 shown inFIG. 1. The plurality of mud pump units in mud pump array 210 areconfigured to collectively draw drilling mud from the suction manifold250, which is in fluid communication with inlet pipe 150 shown in FIG.1, and push drilling mud into discharge manifold 252, which is in fluidcommunication with discharge pipe 152, shown in FIG. 1. According tosome embodiments, each of the pump units in the pump array is apiston-type positive displacement pump and has its own linear electricmotor for reciprocation of the pump piston. In this example, pump units220, 222, 224, 226 and 228 are actuated with a linear electric motors230, 232, 234, 236 and 238, respectively. Also shown in FIG. 2 are pumpsubassemblies 240, 242, 244, 246 and 248 which include suction anddischarge valves for pump units 220, 222, 224, 226 and 228,respectively. According to some embodiments, the pump system 138 can beconfigured such that each of the pump units 220, 222, 224, 226 and 228in the array 210 can be individually brought “on-line” or taken “offline.” In some examples, relative timing of the pump strokes of each ofthe pump units can be altered to accommodate different numbers of pumpunits when operating pump units are added or removed from the array. Inthis way, a modular design can be achieved, such that if one pump unitfails or otherwise needs to be taken off-line it can be hydraulicallyisolated (e.g. using gate valves 350 and 352) and worked on while theremaining pump units continue to operate in the array. This modulardesign can significantly increase equipment availability, and reduce thepotential for excessive non-productive time in the event of an unplannedfailure. Although the example of FIG. 2 shows that the pump arrayconsists of five pump units, in general such arrays can include othernumbers of pump units such as two, three, four, five, six, seven, ormore pump units.

FIGS. 3A, 3B, 3C and 3D are a perspective view, side view, exploded viewand cross section of a linear motor actuated mud pump unit, according tosome embodiments. Shown is further detail of a single pump unit 220,which can form part of a pump array in mud pump system for use in a welldrilling system, such as mud pump array 210 shown in FIG. 2 and mud pumpsystem 138 shown in FIG. 1. A linear electric motor 230 is used toanimate the pump unit. Known motors include linear motors that createlinear motion in response to a control input. According to someembodiments, motor 230 is a tubular-type linear servo motor. Many of thecomponents of the pump unit are visible in the exploded view of FIG. 3C.The linear motor 230 includes a stationary stator 306 and reciprocatingmover rod 308. The stator 306 is energized by a series of coils. Moverrod 308 can include a series of permanent magnets configured to interactwith magnetic forces induced by current in and the arrangement of coilsin stator 306. The mover rod 308 is attached to piston 324 via couplingadapter 312. Piston 324 slides within a central cylindrical opening ofliner 330. A seal 314 is fixed to the end of piston 324 that is sizedand configured to form a seal with the inner surface of liner 330.Stator 306 of motor 230 is mounted on frame 332 which is, in turn,mounted to valve module 340. Within the frame 332, also shown is linerlock 328 and linear lock nut 326. The valve module 340 includes suctionvalve 370 and discharge valve 372 disposed on the upstream anddownstream ends, respectively, of central conduit 342. When the piston324 is actuated by the mover rod 308 as shown by dashed arrows in FIG.3D, alternating low fluid pressure (suction) and high fluid pressure(discharge) is generated within the central conduit 342. The suction anddischarge valves 370 and 372 act to open and close, thereby pumpingfluid from suction conduit 380, through central conduit 342, andoutwards through discharge conduit 382 as shown by the dotted arrows inFIG. 3D. Also visible in FIGS. 3A-D are suction and discharge gatevalves 350 and 352, as well as valve covers 360 and 362.

Pump units such as shown can have one or more advantages overconventional pumps, including: scalability in size, optimal compactnessof size, and increased control precision. Using a linear motor in areciprocating fluid pump as described enables a reduction in the amountof parts on the mud pump itself when compared to conventional mud pumps.Furthermore, mechanical alignment of a linear motor can be achieved moreeasily than with conventional mud pumps. According to some embodimentsusing such a linear motor, a modular design can be achieved, such thatif one unit or “cylinder” fails it can be isolated and worked on whilethe other units or cylinders continue to work. This leads to increasedequipment availability, and reduced the potential for excessivenon-productive time in the event of an unplanned failure. The modulardesign as described herein, according to some embodiments, enables adrilling rig to have as many units or cylinders as needed. The pumpunits/cylinders can added or removed as rig requirements change.

According to some embodiments, the units or cylinders can be mounted inany number of orientations, vertical, horizontal or angular. The linearmotor, with an individual servo motor actuating each piston, enablescontrol over the speed, acceleration and stroke length to higher degreeof precision and repeatability than with known conventional mud pumps.This enhanced precision enables manipulation of the velocity profile ofthe pistons that conventional (e.g. crankshaft type) mud pump designs donot allow because in such designs all the pistons are mechanicallylinked and forced to operate in a sinusoidal way. FIGS. 5A and 5B areplots showing examples of piston velocity profiles for a preciselycontrolled pump piston, according to some embodiments (profile 510 inFIG. 5A), and conventional crankshaft driven pump piston (profile 512 inFIG. 5B.) The linear motor and servo motor-based designed, according tosome embodiments, can therefore allow for timing and control of thepistons individually such that one can significantly reduce or eliminatethe use of pulsation dampeners, which are a costly maintenance item. Thereduction in fluid pulsation can have significant benefits for downholetechnology, which often relies on mud pulse telemetry to transmitvaluable data about downhole conditions. Reduced pump-induced pulsationcan therefore lead to transmission and reception of higherquality/resolution data. This can in turn allow for greater visibilityof downhole conditions, and can result in significant cost savings forthe field operator.

FIG. 4 is a diagram illustrating suppling power and control to a linearservo motor configured to actuate a pump unit, according to someembodiments. A programmable controller 410 sends speed and force controlsignals to module controller 412. Module controller 412 is configured tocontrol the piston position, piston speed and/or piston force accordingto the control signals received from controller 410. According to someembodiments, module controller 412 is configured to send speed voltagereference signals to the drive unit 420. Drive unit 420 is configured toreceive electrical power from power supply 422 and drive the linearservo motor 230 of a pump unit such as pump unit 220 shown in FIG. 2.Voltage and frequency output from drive 420 control the motor 230. Themodule controller 412 can use current feedback to control piston force.

The power supply 422 in many cases will be an AC power supply. In suchcases the drive unit 420 receives power from AC power supply 422 andthrough a converter and inverter, the amplitude and frequency can beadjusted to properly control the servo motor 230. According to someembodiments, the servo motor 230 includes a piston position encoder 430.The encoder 430 can be configure to detect linear motion and/or positionof motor shaft 308. The encoder output can by feed back to modulecontroller 412. Module controller 412 can include speed adjustment,position adjustment and/or current adjustment functionality andcontroller 412 can use feedback from an encoder 430 as shown to moreaccurately control the current from inverter 424. According to someembodiments, a pressure sensor can be mounted on the discharge manifold250 and/or discharge pipe 150 (e.g. sensor 662 in FIG. 6). In such casesthe pressure data can also be used by module controller 412 to moreaccurately control the pump. Using the feedback signal(s), the motorlinear extension/retraction can be controlled so as to minimize oreliminate the error. With the close loop control, the motor 230 cancarry out highly accurate positioning operations.

FIG. 6 is a block diagram illustrating power and control systemsassociated with a modular pumping system that include a plurality ofpump units, according to some embodiments. The control system shown isused to control several pump units, such as pump units 220, 222, 224,226 and 228 shown in FIG. 2. Human-machine interface 610 is shown whichcan include a display screens, knobs, and/or sliders, etc. to allow theoperator to control and adjust the speed and force for the pumpingsystem as well as to monitor condition of the pump units and driveunits. Programmable controller 410 is used for overall control of thepump system, and a system controller 620 is used to control each pumpunit by determining which pump units are active, the positions each pumpas well as to monitor pressure and adjust the system to optimize (orminimize) pressure pulsation. Note that a pressure transducer 662 ispositioned on discharge manifold 252 and/or discharge pipe 152 and sendspressure signals to system controller 620.

System controller 620 is in communication with each of the modulecontrollers 412, 612, 616 and 618. As described with respect to FIG. 4,the module controllers (in this case, 412, 612, 616 and 618) areconfigured to control the drive units (in this case 420, 622, 624, 626and 628). As shown, the module controllers each receive feedback signalsfrom the linear motors and from the pump sub-assemblies. Positionencoder 430 can be used (as described, supra) to detect linear motionand/or position of motor shaft 308 (shown in FIGS. 3C and 3D). Thefeedback from encoder 430 is sent to module controller 412. Similarly,other driver and/or motor status signals 630, 632, 634, 636 and 638include: winding temperature, resistance, bearing temperature, andvibration sensor output. Also shown for the other pump units areencoders 633, 635, 637 and 639. Power supply 422 is also shown whichsupplies AC power to drive units 420, 622, 624, 626 and 628. Also shownin FIG. 6 are the gate valves 350, 352, 653, 656, 654, 655, 656, 657,658 and 659 that are used to allow hydraulic isolation of any of thepump units.

FIGS. 7A, 7B, 7C and 7D are a perspective view, a top view, and twocross sections of a linear motor actuated mud pump unit, according tosome embodiments. In this example, the linear motor 730 has a movingelement configured as a flat plate rather than a tubular shaped rod asshown in FIGS. 2 and 3A-D. The flat linear motor pump unit 720 issimilar in many respects to the pump units 220, 222, 224, 226 and 228shown in FIGS. 2, and much of the description of those pump units andunit 220 in further detail, applies equally to the pump unit 720.According to some embodiments, pump system 138 shown in FIGS. 1 and 2,and pump array 210 shown in FIG. 2, can include a plurality (e.g. 2, 3,4, 5, 6 or more) of pump units 720 instead of pump units 220, 222, 224,226 and 228. According to some embodiments, pump system 138 shown inFIGS. 1 and 2, and pump array 210 shown in FIG. 2, can include acombination of pump units with tubular-type linear motors (such as unit220), and pump units with flat-type linear motors (such as unit 720).The resulting arrays and pump systems will benefit from the sameadvantages (e.g. pulse control, modularity, scalability, cost savings)that are described elsewhere herein. Pumping systems based on aflat-configured motor, as in the case of pump unit 720, especially whenoriented in a horizontal configuration as shown, provide benefits inflexibility of pumping system layout, increased force density, andpossible savings in space and cost for the overall drilling operation.

Pump unit 720 includes a flat linear motor 730 and a pump subassembly740. The linear motor 730 includes a moving plate 708 sandwiched betweentwo stationary stator plates 702 and 704. The stator plates 702 and 704are energized by coils 706 and 707 respectively. Note that the coils 706and 707 continue within stator plates 702 and 704, respectively. Movingplate 708 can include a series of permanent magnets configured tointeract with magnetic forces induced by current in and the arrangementof coils 706 and 707. Moving plate 708 and the attached piston 724 cantranslate side to side as indicated by the dashed arrows. Motion ofplate 708 is guided by linear guide bars 716 and 718 and linear bearings726. Note that there is a small air gap formed at the interfaces betweenstator plate 702 and moving plate 708, and between stator plate 704 andmoving plate 708. A linear sealing element 728 provides isolationbetween the motor 730 and the opening within yoke 732. A seal 714 isfixed to the end of piston 724 that is sized and configured to form aseal with the inner surface of liner 712. The pump subassembly 740includes suction valve 770 and discharge valve 772 disposed on theupstream and downstream ends, respectively, of a central conduit. Theinlet of the pump unit 720 is at a suction port 780, visible in FIG. 7C,and the outlet is through either or both of two discharge ports 782 (oneof which is visible in FIG. 7A). When the piston 724 is actuated by themotor 730 as shown by dashed arrows, alternating low fluid pressure(suction) and high fluid pressure (discharge) is generated within thecentral conduit and within the liner 712. The suction and dischargevalves 770 and 772 act to open and close thereby pumping fluid fromsuction port 780 to discharge ports 782, as shown by the dotted arrows.

FIGS. 8A, 8B, 8C and 8D are a perspective view, a top view, and twocross sections of a linear motor actuated dual-action pump unit,according to some embodiments. In this example, the linear motor 830 ofpump unit 820 is similar or identical to motor 730 shown in FIGS. 7A,7B, 7C or 7D, but is configured to drive two pumping subassemblies 842and 843. The dual-action configuration of pump unit 820 can providesignificant benefits in terms of pumping efficiency. In particulardual-action configurations such as shown can provide higher flow volumefor the amount of pump space. The pump unit 820 is similar in manyrespects to the pump unit 720 shown in 7A, 7B, 7C or 7D and pump units220, 222, 224, 226 and 228 shown in FIGS. 2. Much of the description ofthose pump units applies equally to the pump unit 820. According to someembodiments, pump system 138 shown in FIGS. 1 and 2, and pump array 210shown in FIG. 2, can include a plurality (e.g. 2, 3, 4, 5, 6 or more) ofpump units 820 instead of, or in combination with pump units 720, 220,222, 224, 226 and 228. The resulting arrays and pump systems willbenefit from the same advantages (e.g. pulse control, modularity,scalability, cost savings) that are described elsewhere herein.

Pump unit 820 includes a flat linear motor 830 and two pumpingsubassemblies 842 and 843. The linear motor 830 includes a moving plate808 sandwiched between two stationary stator plates 802 and 804. Thestator plates 802 and 804 are energized by coils 806 and 807respectively. Note that the coils 806 and 807 continue within statorplates 802 and 804, respectively, although not visible in FIGS. 8A, 8B,8C or 8D. Moving plate 808 can include a series of permanent magnetsconfigured to interact with magnetic forces induced by current in andthe arrangement of coils 806 and 807. Moving plate 808 and the attachedpistons 824 and 825 can translate side to side as indicated by thedashed arrows. Motion of plate 808 is guided by linear guide bars 816and 818 and linear bearings 826. Note that there is a small air gapformed at the interfaces between stator plate 802 and moving plate 808,and between stator plate 804 and moving plate 808. A linear sealingelements 828 and 829 provides isolation between the motor 830 and theopening within yokes 832 and 833, respectively. Seals 814 and 815 arefixed to the ends of pistons 824 and 825 respectively, and are sized andconfigured to form a seal with the inner surface of liner 812 and 813,respectively. The pumping subassembly 842 includes suction valve 870 anddischarge valve 872 disposed on the upstream and downstream ends,respectively, of a central conduit connected to the cylinder withinliner 812. Similarly, the pumping subassembly 843 includes suction valve871 and discharge valve 873 disposed on the upstream and downstreamends, respectively, of a central conduit connected to the cylinderwithin liner 813. The inlet of pumping subassembly 842 is at a suctionport 880, and the outlet is through either or both of two dischargeports 882. The inlet of pumping subassembly 843 is at a suction port881, and the outlet is through either or both of two discharge ports883. When the pistons 824 and 825 are actuated by the motor 830 as shownby dashed arrows, alternating low fluid pressure (suction) and highfluid pressure (discharge) is generated within the central conduits ofpumping subassemblies 842 and 843. The suction and discharge valves 870,871, 872 and 873 act to open and close thereby pumping fluid fromsuction ports 880 and 881 to discharge ports 882 and 883 as shown by thedotted arrows. Also shown in FIGS. 7D and 8D are alternate bearingpositions 790 and 890, respectively.

Although the tubular-type linear motors are described herein and areshown in FIGS. 2, 3A, 3B, 3C and 3D as vertically oriented, according tosome embodiments, such linear motors can be oriented horizontally, suchthat the moving rod and piston translate in a primarily horizontalrather than vertical direction. Although the tubular-type linear motorsare described herein and are shown in FIGS. 2, 3A, 3B, 3C and 3D asbeing single-action, according to some embodiments, such tubular-typelinear motors can be adapted to dual action (i.e. alternativelysuctioning and pressurizing two opposing cylinders) similar to thatshown in FIGS. 8A, 8B, 8C and 8D. Furthermore, although the linearmotors have been described thus far as either tubular-type or flat-type,according to some embodiments other types and shapes of linear motorscan be used.

While the disclosure may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the disclosure is not intended tobe limited to the particular forms disclosed. Rather, the disclosure isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the disclosure as defined by the followingappended claims.

The techniques presented and claimed herein are referenced and appliedto material objects and concrete examples of a practical nature thatdemonstrably improve the present technical field and, as such, are notabstract, intangible or purely theoretical. Further, if any claimsappended to the end of this specification contain one or more elementsdesignated as “means for” or “step for” performing a function, it isintended that such elements are to be interpreted under 35 U.S.C.112(f). However, for any claims containing elements designated in anyother manner, it is intended that such elements are not to beinterpreted under 35 U.S.C. 112(f). While the subject disclosure isdescribed through the above embodiments, it will be understood by thoseof ordinary skill in the art, that modification to and variation of theillustrated embodiments may be made without departing from the conceptsherein disclosed.

What is claimed is:
 1. A pump system configured to pump fluid down awellbore, the system comprising: an electrically-powered linear motorincluding a stationary portion and a moving portion, the moving portionadapted to move in a reciprocating fashion relative to the stationaryportion; and a pump assembly including a piston and one or more valvesconfigured to pump a fluid into a wellbore, the piston being driven bythe reciprocating moving portion.
 2. A pump system according to claim 1further comprising: a sensor configured to detect movement and/orposition of at least a portion of the motor and/or pump assembly andoutput position information; and a control system configured to controlthe motion of linear motor, to receive the position information and tomake adjustments the control based at least in part on the positioninformation thereby reducing error in said motion.
 3. A pump systemaccording to claim 2 wherein said control system is further configuredto reducing flow pulsation of fluid pumped by the pump system based atleast in part on said position information.
 4. A pump system accordingto claim 3 further comprising a pressure sensor configured to detectdischarge fluid pressure of the pump system and output pressureinformation, and said reducing flow pulsation of fluid pumped by thepump system is further based at least in part on said pressureinformation.
 5. A pump system according to claim 2 said motor and saidpump assembly together form a pump unit, and said system furthercomprising one or more additional pump units, each of which includes atleast one linear motor and at least one pump assembly, and wherein saidcontrol system is further configured to adjust relative timing of eachmotor based on a total number of pump units in the pump system.
 6. Apump system according to claim 1 wherein the moving portion isrod-shaped and the stationary portion is tube-shaped and surrounds therod-shaped moving portion.
 7. A pump system according to claim 6 whereinthe rod-shaped moving portion is vertically oriented and is configuredto move in a vertical direction.
 8. A pump system according to claim 1wherein the moving portions and the stationary portions are rectangularand planar in shape, and the stationary portion includes two planarportions disposed on either side of and sandwiching the moving portion.9. A pump system according to claim 8 wherein the moving portion isconfigured to move primarily in horizontal direction.
 10. A pump systemaccording to claim 1 further comprising a second pump assembly includinga second piston and a set of second valves configured to pump the fluidinto the wellbore, the second piston being driven by said reciprocatingmoving portion.
 11. A pump system according to claim 10 furthercomprising a plurality of isolation valves positioned and configured tohydraulically isolate either of said pump assembly or said second pumpassembly thereby facilitating servicing and/or replacement of pumpsystem components without loss of pump system operation.
 12. A pumpsystem according to claim 1 wherein said fluid is selected from a groupconsisting of: drilling mud, circulation fluid, and fracturing fluid.13. A method of pumping a fluid into a wellbore comprising: controllinga first electrically-powered linear motor that includes a stationaryportion and a moving portion, such that the moving portion moves in areciprocating fashion relative to the stationary portion and drives afirst pump assembly that includes a piston and one or more valves,thereby causing a fluid to flow into the wellbore; receiving positioninformation from a sensor configured to detect movement and/or positionof at least a portion of the motor and/or pump assembly; and adjustingsaid controlling based at least in part on the position informationthereby reducing error in said controlling.
 14. A method according claim13 wherein said first motor and said first pump assembly together form afirst pump unit, and said controlling includes controlling a pluralityof additional pump units, said first pump unit and said additional pumpunits forming a pump system.
 15. A method according to claim 14 furthercomprising: altering the number of pump units being controlled; andadjusting relative timing of each motor based on a new total number ofpump units in the pump system.
 16. A method according to claim 14further comprising receiving pressure information from a sensorconfigured to detect pressure of the fluid being discharged from saidpump system, and said controlling further includes controlling saidfirst pump unit and said plurality of additional pump units to reducepressure pulsations bases at least in part on information from saidpressure sensor.
 17. A method according to claim 16 wherein saidreducing pressure pulsations is achieved at least in part by controllingpiston velocity profiles of each pump unit and phase angles between thepump units.
 18. A method according to claim 13 wherein the pump saidmoving portion of the first electrically-powered linear motor furtherdrives a second pump assembly including a second piston and a set ofsecond valves configured to pump the fluid into the wellbore.
 19. Amethod according to claim 13 wherein said fluid is selected from a groupconsisting of: drilling mud, circulation fluid, and fracturing fluid.